Supreme Court Justice Oliver Wendell Holmes said there were "phrases that serve as an excuse for not thinking." One of these phrases that substitute for thought today is one that depicts the current problems of blacks in America as "a legacy of slavery."

New York Times writer Nicholas Kristof asserts that there is "overwhelming evidence that centuries of racial subjugation still shape inequity in the 21st century" and he mentions "the lingering effects of slavery." But before we become overwhelmed, that evidence should be checked out.

The evidence offered by Mr. Kristof in the November 16th issue of the New York Times seems considerably short of overwhelming, to put it charitably. He cites a study showing that "counties in America that had a higher proportion of slaves in 1860 are still more unequal today." Has he never heard statisticians' repeated warnings that correlation is not causation?

The South long remained a region that blacks fled by the millions -- for very good reasons. But, in more recent years, the net migration of blacks has been from the North to the South. No doubt they have good reasons for that as well.

But there is no reason to believe that blacks today are unaware of the history of slavery or of the Jim Crow era in the South. Indeed, there are black "leaders" who seem to talk about nothing else. Yet blacks who are moving back to the South seem more concerned with the present and the future than with the past.

Kristof's other "overwhelming" evidence of the current effects of past slavery is that blacks do not have as much income as whites. But Puerto Ricans do not have as much income as Japanese Americans. Mexican Americans do not have as much income as Cuban Americans. All sorts of people do not have as much income as all sorts of other people, not only in the United States, but in countries around the world. And most of these people were never enslaved.

If we wanted to be serious about evidence, we might compare where blacks stood a hundred years after the end of slavery with where they stood after 30 years of the liberal welfare state. In other words, we could compare hard evidence on "the legacy of slavery" with hard evidence on the legacy of liberals.

Despite the grand myth that black economic progress began or accelerated with the passage of the civil rights laws and "war on poverty" programs of the 1960s, the cold fact is that the poverty rate among blacks fell from 87 percent in 1940 to 47 percent by 1960. This was before any of those programs began.

Over the next 20 years, the poverty rate among blacks fell another 18 percentage points, compared to the 40-point drop in the previous 20 years. This was the continuation of a previous economic trend, at a slower rate of progress, not the economic grand deliverance proclaimed by liberals and self-serving black "leaders."

Ending the Jim Crow laws was a landmark achievement. But, despite the great proliferation of black political and other "leaders" that resulted from the laws and policies of the 1960s, nothing comparable happened economically. And there were serious retrogressions socially.

Nearly a hundred years of the supposed "legacy of slavery" found most black children being raised in two-parent families in 1960. But thirty years after the liberal welfare state found the great majority of black children being raised by a single parent.

The murder rate among blacks in 1960 was one-half of what it became 20 years later, after a legacy of liberals' law enforcement policies. Public housing projects in the first half of the 20th century were clean, safe places, where people slept outside on hot summer nights, when they were too poor to afford air conditioning. That was before admissions standards for public housing projects were lowered or abandoned, in the euphoria of liberal non-judgmental notions. And it was before the toxic message of victimhood was spread by liberals. We all know what hell holes public housing has become in our times. The same toxic message produced similar social results among lower-income people in England, despite an absence of a "legacy of slavery" there.

If we are to go by evidence of social retrogression, liberals have wreaked more havoc on blacks than the supposed "legacy of slavery" they talk about. Liberals should heed the title of Jason Riley's insightful new book, "Please Stop Helping Us."